The accumulation of karyophilic proteins, molecules which are highly concentrated in the nucleus, appears to involve nuclear binding and, in some instances, facilitated transport across the envelope. We wish to investigate these proceses (nuclear binding and transport) in oocytes, using nucleoplasmin as a model. Nucleoplasmin is a large endogenous oocyte protein (165,000 daltons) that has a nucleus to cytoplasmic concentration ratio of over 400. It is also known to be transported through the pores. Studies are proposed to establish the location of the transport and binding domains that are present on nucleoplasmin and determine if similar functional sites are associated with other oocytes nuclear proteins. In addition, experiments have been designed to identify the nuclear binding site(s) required for the accumulation of nucleoplasmin and, perhaps, other karyophilic polypeptides. Finally, we hope to determine if the transport process is reversible. These experiments are centered around in vivo procedures and involve the microinjection of affinity purified antibodies against nucleoplasmin and binding proteins.